1. Field of the Invention
The present invention relates to a solid-electrolyte fuel cell and a method for manufacturing the solid-electrolyte fuel cell.
2. Description of the Related Art
A solid-electrolyte fuel cell comprises a plurality of three-layered films each being a fuel electrode, a solid-electrolyte film and an air electrode. Each three-layered film has a flat plate shape and is conventionally supported by either a self-standing film system or a supported film system.
In the self-standing film system, as indicated in the fragmentary sectional view of the three-layered film in FIG. 1, a solid-electrolyte film 2 thicker than each of the fuel electrode 1 and air electrode 3 of the three-layered film 4 comprising the fuel cell supports the structure of the three-layered film 4.
In the supported film system, the structure of the three-layered film is supported by parts other than the solid-electrolyte film, and as indicated in the fragmentary sectional view of the three-layered film in FIG. 2A, the structure of the three-layered film 4 can be supported by setting the thickness of the air electrode 3 larger than that of the fuel electrode 1 and the solid-electrolyte film 2, or setting the thickness of the fuel electrode 1 to be larger than that of the solid-electrolyte film 2 and the air electrode 3 as indicated in FIG. 2B.
Although the self-standing film system is simple in structure, there has been the problem that the internal resistance of the cell becomes large because the solid-electrolyte film is thick.
In the supported film system, the thickness of the solid-electrolyte film itself can be reduced, and the internal resistance of the cell can be controlled to be low. However, the material of the air electrode of (La, Sr) MnO.sub.3 is lower in strength than the YSZ (yttrium stabilized zirconia) generally used for the material of the solid-electrolyte film, and the air electrode is porous to permit the air gas to pass through the electrode. Therefore, when the air electrode is used for the support layer, for example, its thickness must be fairly large so that a supporting strength equivalent to that of the solid-electrolyte film in the self-standing film system is provided. This is the same with the case where the fuel electrode is the support layer in place of the air electrode.
Thus, the cell which is the basic unit of power generation of the fuel cell is thicker in the case of the supported film system than that of the self-standing film system, and as a result, there is a problem in that the volume of the solid-electrolyte fuel cell is increased. At the same time, the electric characteristics of the electrode and the reactivity with the solid-electrolyte film with which the electrode is bonded must be taken into full consideration, and it has been difficult to regulate the coefficient of thermal expansion of the interconnector added to electrically connect adjacent cells to each other by supplying the gas to the electrodes under consideration.
In view of the forgoing, there is a need for a solid-electrolyte fuel cell having a supporting strength similar to that of the structure where the solid-electrolyte film is the support layer although the solid-electrolyte film is not the support layer, the increase of the volume is controlled, and the coefficient of thermal expansion between the support layer and the interconnector can be easily regulated. There is also a need for a method for manufacturing the solid-electrolyte fuel cell.